The present invention relates to a surgical instrument for performing a sinus lift in particular a crestal sinus lift.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Sinus lift involves a surgical procedure in which the membrane of the maxillary sinus is partly detached and lifted from the jawbone to provide a space between bone and maxillary sinus membrane. Inserted into the provided space is an autologous bone, e.g. from the Tuber maxillae, the Linea oblique, the chin region, or from the iliac crest (bone replacement materials, bone chip) or a synthetic bone replacement material, e.g. bone replacement material, commercially available by Geistlich AG under the trade name Bio-Oss, oftentimes blended with autologous bone. This material is intended to transform into bone within 6 months to ensure a solid foundation for an implant.
The conventional procedure for a sinus lift requires preparation of a mucoperiosteal flap in the buccal molar region and to cut an oval window in the thus exposed bone, without damage to the subjacent maxillary sinus membrane. The oval-shaped bone disk hanging from the maxillary sinus membrane is then gently pressed in a direction of the maxillary sinus, while the membrane is separated from the bone around the window with the aid of special instruments. As the maxillary sinus membrane is very delicate, comparable to an egg skin, this procedure is being executed very carefully because of the risk to damage the maxillary sinus membrane. The space provided in this manner in the maxillary sinus is then filled with bone replacement material through the window and the buccal window is covered with a film. The film is normally made of absorbable material, e.g. a membrane which is commercially available by Geistlich AG under the trademark Bio-Gide. Subsequently, the mucoperiosteal flap is sealingly sutured. The procedure is very invasive and subjects the patient to great stress as a result of substantial swelling and discoloration of up to 10 days, and possibly of pain.
This surgical procedure is oftentimes referred to as “open” or “classic” sinus lift. If sufficient residual bone height is available, approximately at a height of 5 mm, implants can be inserted simultaneously with the sinus lift (single-stage sinus lift). The implants can be fully strained only after the bone replacement material has hardened. When the residual bone height is too low, the implants are inserted in a second surgery about 6-8 months following the sinus lift (two-stage sinus lift).
The so-called crestal sinus lift is oftentimes carried out without folding of a bone plate. The access to the maxillary sinus is made possible from the maxillary crest. The mucous membrane of the mouth is hereby opened from the toothless part of the maxillary crest up to the bone and the bone is scraped by a cylindrical cutter in the shape of a tunnel up to slightly underneath the maxillary sinus membrane. A cylindrical instrument is then carefully tapped in a direction of the maxillary sinus so that a thin bone disk is pressed in the direction of the maxillary sinus, whereby the maxillary sinus membrane adheres upon the top of bone disk. The maxillary sinus membrane is hereby lifted in the form of a tent and tensed. As the bore is too small (diameter of about 4 mm), there is no possibility to separate the maxillary sinus membrane with instruments from the bone around the bore. After the maxillary sinus membrane has been elevated, bone replacement material is introduced via the bore. The surgery may also be performed in two separate stages or simultaneously. This minimally invasive procedure is however limited to cases which require only slight buildup of bone height for insertion of the implant.
Another instrument allows realization of a greater cavity during the crestal sinus lift and involves a balloon which is introduced through the bore to the pointed end of the instrument and gently inflated so that the maxillary sinus membrane separates from the bone. As the force is applied only at the tip of the balloon upon the maxillary sinus membrane, it is not possible to evenly distribute the tension so that a premature rupture (bursting) of the maxillary sinus membrane can occur.
Published European Patent Appl. No. EP 1 362 561 A1 describes an apparatus for preparation of a sinus bottom elevation. A pump is connected to a fluid source and conveys a controlled volume of fluid for injection into the maxillary sinus. The sinus membrane is hereby elevated by the jet of fluid flowing through the access port and separated from the jawbone. A sensor measures pressure values in the flow path of the fluid. A perforation of the maxillary sinus membrane can be deduced from changes in the pressure values. Even when this jet is only gentle in nature, the use of a fluid jet causes pressure peaks at those sites where the jet impacts the sinus membrane. Elevation of the sinus membrane is possible only through the application of the fluid jet because of the underpressure in the interior as a result of a sealing of the outer bore end by means of suction cups. Thus, it is not possible to build up excess pressure in the cavity to be expanded, without the suction cup losing effectiveness and falling off.
German Pat. No. DE 103 22 869 B3 describes a device for carrying out a sinus bottom elevation, using a treatment instrument for creating an access or an insertion channel in the jaw being treated. The device has a pulsating pressure medium source connected to the treatment instrument which is provided with at least one pressure medium feed and a pressure medium outlet over its length. Separation of the sinus membrane is hereby effected by a pulsating flushing by which an absorbable membrane inserted through the bore should be unfolded, like an umbrella, between sinus membrane and inlet port. This procedure is required because, on one hand, there is hardly any possibility to control the internal pressure as a result of the drainage, and, on the other hand, the direct impact of a flushing pulse upon the sinus membrane may easily cause injury thereof. This known device has also other shortcomings. Firstly, any damage to the sinus membrane will remain essentially unrecognized during lifting of the sinus membrane. Secondly, the unfolding of the absorbable membrane and thus the assumption of a correct disposition cannot be monitored or influenced. Thirdly, the internal pressure increases and the sinus membrane ruptures, when the drainage of fluid from the maxillary sinus membrane is clogged.
International Publ. No. WO 2006/044073 describes an apparatus for installing a dental implant in the alveolar ridge and including a sleeve which is inserted through the alveolar ridge to the maxillary sinus. A source of flowing material is positioned at the lower end of the sleeve and injects flowing material through the sleeve into a cavity between the ridge and the subantral membrane to thereby increase bone mass. This apparatus has the drawback that the sinus membrane is separated from the bone solely by the effect of the hydrostatic pressure. As soon as a point is reached when the sinus membrane no longer can separate from the bone, pressure needs to be increased, quickly reaching the stress limit of the sinus membrane.
FIGS. 1 and 2 show schematically a conventional method for performing a sinus lift. A laterally prepared bone plate 17 is hereby pressed into the maxillary sinus and folded upwardly like a flap to detach the maxillary sinus membrane 7 from the bone and to thereby form a body cavity 6 beneath the bone plate 17. Special instruments can be inserted through a comparably large bone window 20 to separate the maxillary sinus membrane 7 from the jawbone 8. Bone replacement material is then filled through the window 20 into the body cavity 6, while the bone plate 7 remains in the cavity. The bone window 20 is then closed by an absorbable film and the initially detached mucoperiosteal flap is securely stitched over it.
It would therefore be desirable and advantageous to provide an improved surgical instrument to obviate prior art shortcomings.